The present invention relates generally to the field of forming a bell or sockets in the end of a length of plastic pipe, and more particularly, is directed to an automatic, pressurized, sealed forming apparatus capable of producing sharply defined bells on plastic pipe regardless of wall thickness.
It is the present practice to utilize known types of plastic pipe forming apparatus to provide a bell shape in one end of each length of pipe to allow joints in adjacent lengths of plastic pipe to be readily made in the field by utilizing known techniques and existing tools. The presently available pipe belling machines usually incorporate a means to heat one end of the plastic pipe prior to belling to soften the plastic, a mandrel means to shape the interior of the bell at the heated pipe end and external clamps to shape the exterior periphery of the belled end during the belling process. The prior art devices usually also incorporate suitable cooling means to set the shaped end after belling in a relatively rapid manner to provide efficient utilization of the machine and to reduce time requirements and production costs.
It is now increasingly popular and necessary to provide an interior groove in the bell as the pipe bell is formed to accommodate a sealing gasket which can be applied within the groove to quickly and automatically seal the pipe joint when adjacent lengths of pipe are joined together. To form such an internal groove, it is the common practice to provide a plurality of expanding and contracting cooperating segments within the mandrel construction to thereby permit the mandrel to automatically and simultaneously form both the interior configuration of the pipe bell and also the interior peripheral groove.
It will be appreciated that wall thicknesses of plastic pipes vary widely from pipe to pipe due to the design requirements of such parameters as pipe diameter, type of service of the pipe, the type of plastic employed in fabricating the pipe, pressure requirements and other such design considerations. Due to the variances in wall thickness of the different plastic pipes which are presented to a belling fabricator for pipe belling purposes, each mandrel for each diameter of pipe previously had to be equipped with various sized external clamps, which clamps were specifically designed and configured for a particular pipe wall thickness. Accordingly, it was possible for one mandrel to require several sets of clamps in order to make a machine relatively universally adaptable for the pipes normally treated by a single plant. In other instances, additional tooling costs were involved in carefully machining the clamps to assure forming bells with minimum acceptable wall thickness throughout the entire bell, including the critical area in and about the internal groove. Because of this, tooling and equipment costs have become quite expensive when utilizing existing machines to form pipe bells by employing the combination of a mandrel with external clamps.
Additionally, the external clamps have proved to be deficient to a degree in that the use of such external clamps has usually resulted in marring the external periphery of the belled end of the pipe due to imperfections in the surfaces of the clamps, and imperfections in the mating surfaces of the cooperating upper and lower clamp halves due to misalignment of the parts during the bell forming operations.